European Patent Publication 0 178 951 (Grantham) shows a convertible hospital bed in which an upper bed frame, bearing a mattress, which is movable over a lower bed frame towards the foot of the bed while elevating the trunk of the occupant. In this way the occupant arrives at the foot of the bed in an upright seated position. In this case the bed serves as a stable framework on which the occupant can readily be moved. Grantham acknowledges that the invention is for beds of the `hospital` type `being particularly designed for use in hospitals and nursing homes or for residential use with patients who are possibly ambulatory but too weak or incapacitated to get into and out of bed without assistance`. Grantham does not suggest that the bed can usefully be operated by the occupant.
U.S. Pat. No. 4,613,997 (Langdale) discloses a convalescent bed with a base frame and support frame for a mattress pivotally mounted for movement between horizontal and vertical positions. The support frame provides a support portion for the trunk and legs and a hinged portion for the head. The bed is provided with power mechanism to move the support frame as a unit between horizontal and vertical positions. No seating position is provided. As in EPO 0178951 Langdale relies on the structural support provided by a full size bed frame during movement of the support frame. The bed disclosed by Langdale also requires operation by skilled staff.